Got exception when running main on a __init__.py file with flake8 installed

[will133]

Was running pytest 3.10 and now when I try to just run on a module's __init__.py, I'd get an error such as:

$ pytest tests/__init__.py
========================================================= test session starts =========================================================
platform linux -- Python 3.6.7, pytest-3.10.0, py-1.7.0, pluggy-0.8.0
rootdir: /auto/cnvtvws/wlee/fcnvt/blahblah, inifile: setup.cfg
plugins: flake8-1.0.2
collected 0 items / 1 errors

=============================================================== ERRORS ================================================================
__________________________________________________________ ERROR collecting  __________________________________________________________
/myenv/miniconda/envs/test_pytest/lib/python3.6/site-packages/_pytest/runner.py:212: in __init__
    self.result = func()
/myenv/miniconda/envs/test_pytest/lib/python3.6/site-packages/_pytest/runner.py:272: in <lambda>
    call = CallInfo(lambda: list(collector.collect()), "collect")
/myenv/miniconda/envs/test_pytest/lib/python3.6/site-packages/_pytest/main.py:478: in collect
    for x in self._collect(arg):
/myenv/miniconda/envs/test_pytest/lib/python3.6/site-packages/_pytest/main.py:568: in _collect
    yield next(m[0].collect())
/myenv/miniconda/envs/test_pytest/lib/python3.6/site-packages/_pytest/nodes.py:429: in collect
    raise NotImplementedError("abstract")
E   NotImplementedError: abstract
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
======================================================= 1 error in 0.17 seconds =======================================================

It seems like there's new code in _pytest/main.py:563 that has something like:

            # If __init__.py was the only file requested, then the matched node will be
            # the corresponding Package, and the first yielded item will be the __init__
            # Module itself, so just use that. If this special case isn't taken, then all
            # the files in the package will be yielded.
            if argpath.basename == "__init__.py":
                yield next(m[0].collect())
                return

It turns out the m is a list from the previous collect where the first item is actually a Flake8Item. It would not work when you call collect on it. I'm not sure the intention of this extra collect, but should it check if the item isinstance a package?

pip list:

Package        Version
-------------- ----------
atomicwrites   1.2.1
attrs          18.2.0
certifi        2018.10.15
flake8         3.6.0
mccabe         0.6.1
more-itertools 4.3.0
pip            18.1
pluggy         0.8.0
py             1.7.0
pycodestyle    2.4.0
pyflakes       2.0.0
pytest         3.10.0
pytest-flake8  1.0.2
setuptools     40.5.0
six            1.11.0
wheel          0.32.2

I'm using conda to install this:

$ conda create -n test_pytest python=3.6 pytest pytest-flake8

[blueyed]

Duplicate of #4344 ?
(closing already, but feel free to re-open)